The present invention relates to a nonaqueous electrolytic solution containing a specific silicon compound and a nonaqueous secondary battery containing the same. More particularly, it relates to a nonaqueous electrolytic solution containing the silicon compound and capable of providing a battery which shows reduced changes in electrical capacity and internal resistance in charge and discharge cycle repetition and undergoes a reduced change in internal resistance at low temperature and thereby maintains high electrical capacity, namely, a battery excellent in cycle characteristics and low-temperature characteristics. The present invention also relates to a nonaqueous secondary battery comprising the nonaqueous electrolytic solution.
With the recent spread of portable electronic equipment such as portable personal computers and handy video cameras, nonaqueous secondary batteries realizing high voltage and high energy density have enjoyed wide use as a power source of such equipment. There will be a growing demand for nonaqueous secondary batteries applied to electric vehicles and gas-and-electric powered hybrid vehicles that are now being put to practical use from the standpoint of environmental conservation.
However, the state-of-the-art nonaqueous secondary batteries lack reliability as a stable power source because they undergo reduction of capacity and increase of internal resistance when used in low temperature or repeatedly charged and discharged.
Various additives have been proposed for improving performance stability or electric characteristics of nonaqueous secondary batteries. For example, JP-A-10-326611 teaches use of tetramethyl silicate as an organic solvent of a nonaqueous electrolytic solution. The battery proposed exhibits improved cycle characteristics but has the capacity reduction problem. JP-A-10-55822 proposes a flame-retardant electrolytic solution which comprises a silane compound, e.g., octyltriethoxysilane, as a flame-retardant organic solvent. While showing improved flame resistance, this technique is still unsatisfactory in electric characteristics. JP-A-11-16602 discloses an electrolytic solution containing an organosilicon compound having an Si—N bond. This technique succeeds to some extent in preventing generation of hydrohalogenic acid due to water's entering and thereby preventing deterioration of a battery in some extent but is not sufficiently satisfactory in cycle characteristics. JP-A-2002-134169 discloses an electrolytic solution containing a silicon compound having an unsaturated bond. While excellent in cycle characteristics and low-temperature characteristics, this electrolytic solution is insufficient in stability in long-term use.